Optical glass

ABSTRACT

A high refraction low dispersion optical glass, the components thereof including, by weight percentage: B 2 O 3 : 1-30%; SiO 2 : 0-20%; La 2 O 3 : 25-55%; Gd 2 O 3 : 5-40%; Y 2 O 3 : 0-25%; Yb 2 O 3 : 0-10%; Ta 2 O 5 : 0-10%; Nb 2 O 5 : 1-30%; TiO 2 : 0-10%; ZrO 2 : 0.5-20%; WO 3 : 0-10%; ZnO: 0-15%; R 2 O: 0-10%; RO: 0-10%; Al 2 O 3 : 0-10%; GeO 2 : 0-10%; Bi 2 O 3 : 0-10%. A high refraction low dispersion environmentally friendly optical glass having excellent light transmittance may be obtained by reducing the Ta 2 O 5  content within the glass components and introducing suitable amounts of rare earth oxide components having a high refraction low dispersion effect.

TECHNICAL FIELD

The invention relates to an optical glass with high refractive index and low dispersion, and a glass preform and an optical element made of the above optical glass.

BACKGROUND

A lens made of high-refraction low-dispersion optical glass and a lens made of high-refraction high-dispersion optical glass can be combined for chromatic aberration correction and optical system miniaturization. Especially, the market demands on the high-refraction low-dispersion environmental optical glass with refractive index nd of 1.86-1.92 and Abbe number νd of 36-42 are increasing.

JP2001-348244, JP2007-269584 and CN101386469A discloses such high-refraction low-dispersion optical glass, and the optical glass component with the refractive index of more than 1.86 in the embodiments of the Description contains a lot of Ta₂O₅, while Ta₂O₅ belongs to an expensive rare earth oxide. Thus, to inhibit the cost of high-refractive index and low-dispersion optical glass material from increasing, it is hopeful to reduce the content of Ta₂O₅. Meanwhile, the optical element of the optical system for camera shooting or projecting, etc. has higher requirements for the transmittance of optical glass, and the transmission light of the optical system will be affected if the transmission light of the lens formed by high-refraction low-dispersion optical glass is not enough, therefore optical glass is hopeful to have an excellent transmittance.

SUMMARY

The technical problem to be solved by the present invention is to provide a high-refraction low-dispersion optical glass with glass refractive index of more than 1.85 and Abbe number of 35-45. The glass contains no PbO, and has an excellent transmittance when the content of Ta₂O₅ in a glass component is reduced.

The present invention also provides a glass preform and an optical element made of the above optical glass.

To solve the technical problem, the technical scheme of the present invention provides: An optical glass, comprising by weight percentage: B₂O₃: 1-30%; SiO₂: 0-20%; La₂O₃: 25-55%; Gd₂O₃: 5-40%; Y₂O₃: 0-25%; Yb₂O₃: 0-10%; Ta₂O₅: 0-10%; Nb₂O₅: 1-30%; TiO₂: 0-10%; TiO₂/Nb₂O₅: less than 0.3; ZrO₂: 0.5-20%; WO₃: 0-10%; ZnO: 0-15%; (ZnO+Y₂O₃)/La₂O₃: less than 0.5; R₂O: 0-10%, in which R₂O is one or more of Li₂O, Na₂O or K₂O; RO: 0-10%, in which, RO is one or more of BaO, SrO, MgO or CaO; Al₂O₃: 0-10%; GeO₂: 0-10%; Bi₂O₃: 0-10%; the glass contains no PbO; the glass refractive index is more than 1.85, and the Abbe number is 35-45.

The optical glass further contains Sb₂O₃: 0-1%; SnO₂: 0-1%; CeO₂: 0-1%.

It contains B₂O₃: 5-25% and/or SiO₂: 0.1-15% and/or La₂O₃: 30-52% and/or Gd₂O₃: 5-35% and/or Y₂O₃: 1-20% and/or Ta₂O₅: 0-5% and/or Nb₂O₅: 2-25% and/or TiO₂: 0.1-5% and/or ZrO₂: 1-15% and/or WO₃: 0-5% and/or ZnO: 0-10% and/or R₂O: 0-5% and/or RO: 0-5% and/or Al₂O₃: 0-5% and/or GeO₂: 0-5% and/or Bi₂O₃: 0-5% and/or Sb₂O₃: 0-0.5% and/or SnO₂: 0-0.5% and/or CeO₂: 0-0.5%.

SiO₂/(SiO₂+B₂O₃) is less than 0.5; and/or Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is less than 0.2; and/or Nb₂O₅≥ZrO₂; and/or Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) ranges from 0.4 to 0.8; and/or (Nb₂O₅+Ta₂O₅+ZrO₂)/(SiO₂+B₂O₃) is less than 1; and/or (ZnO+Y₂O₃)/La₂O₃ ranges from 0.05 to 0.3.

SiO₂/(SiO₂+B₂O₃) ranges from 0.25 to 0.4; and/or Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is 0.05-0.12; and/or Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) ranges from 0.48 to 0.6; and/or (Nb₂O₅+Ta₂O₅+ZrO₂)/(SiO₂+B₂O₃) ranges from 0.1 to 0.9; and/or (ZnO+Y₂O₃)/La₂O₃ ranges from 0.08 to 0.15.

(Nb₂O₅+Ta₂O₅+ZrO₂)/(SiO₂+B₂O₃) ranges from 0.5 to 0.8.

The glass refractive index ranges from 1.87 to 1.91; the Abbe number ranges from 37 to 41.

The glass refractive index ranges from 1.88 to 1.90; the Abbe number ranges from 38 to 40.

A glass preform is made of the above-mentioned optical glass.

An optical element is made of the above optical glass.

The advantages of the present invention are as follows: The high-refractive index and low-dispersion environmental optical glass with excellent transmittance, as well as a glass preform and an optical element made of the optical glass can be obtained by lowering the content of Ta₂O₅ in the component, and then introducing an approximate amount of such rare earth oxide components with high refraction and low dispersion as La₂O₃, Gd₂O₃, Y₂O₃ and Yb₂O₃ as well as an approximate proportion of one or more of Nb₂O₅ or TiO₂, optimizing the proportions of these components, and the glass containing no PbO.

DETAILED DESCRIPTION

I. Optical Glass

The composition of the optical glass provided by the present invention will be described in detail below, and the ratio of the content to the total content of each glass component is expressed by weight percentage unless otherwise the content and the total eight of each glass component are specified. In the following description, if referred to below or above the prescribed value, the prescribed value is included.

B₂O₃ is a glass network forming component having effects of improving glass meltability and reducing glass transition temperature. In order to achieve the above-mentioned effects, the present invention introduces 1% or more of B₂O₃. However, when the introduced amount is more than 30%, the glass stability will be lowered and the refractive index will be lowered, so that the high refractive index of the present invention cannot be obtained. Therefore, the content of B₂O₃ in the present invention is 1-30%, preferably 5-25%, and more preferably 7-20%.

SiO₂ has an effect of improving the heat stability of glass, and can increase the viscosity in glass melting and forming. However, if the content exceeds 20%, the glass will be hard to melt, and the refractive index required for the present invention cannot be obtained. Therefore, the content of SiO₂ in the present invention is 0-20%, preferably 0.1-15%, and more preferably 3-12%.

To improve the glass meltbility, maintain the glass stability and keep the viscosity applicable to forming molten glass, the content of SiO₂ introduced into the present invention shall be less than or equal to the content of B₂O₃, i.e. SiO₂≤B₂O₃.

In the meantime, to obtain glass with high transmittance, inhibit the glass melting temperature from rising, reduce and prevent the mixture of platinum ions molten into molten glass from making coloring deteriorate, and effectively adjust the Abbe number of glass in the present invention, the SiO₂/(SiO₂+B₂O₃) in the present invention will be preferably less than 0.5, more preferably 0.1-0.45, and further preferably 0.25-0.4.

La₂O₃ is an essential component for obtaining the optical properties required for the present invention. When the content of La₂O₃ is less than 25%, it is difficult to achieve the required optical properties; but when its content exceeds 55%, the glass devitrification resistance and melting properties are deteriorated. Therefore, the content of La₂O₃ in the present invention is 25-55%, preferably 30-52%, and more preferably 35-50%.

The stability of the glass can be improved through coexistence of Gd₂O₃ and La₂O₃ in the present invention, but when the content of Gd₂O₃ is lower than 5%, the above effect is not obvious; when its content exceeds 40%, the glass devitrification resistance is reduced, and the glass stability is worsened. Therefore, the content of Gd₂O₃ in the present invention is 5-40%, preferably in the range of 5-35%, more preferably in the range of 10-30%.

The high-refraction and low-dispersion component of the present invention is also preferably introduced into Y₂O₃, which can improve the meltability and devitrification resistance of the glass. In addition, it can reduce the upper limit of devitrification temperature of the glass, but if its content exceeds 25%, the glass stability and devitrification resistance will be decreased. Thus, the Y₂O₃ content is in the range of 0-25%, preferably in the range of 1-20%, more preferably 2-15%.

Yb₂O₃ is also a high-refractive index and low-dispersion component of the glass in the present invention. When its content exceeds 10%, the glass stability and devitrification resistance will be decreased, so the content of Yb₂O₃ is preferably in the range of 0-10%. Meanwhile, compared with Gd₂O₃, Y₂O₃, Yb₂O₃ is more expensive, and has a little effect on improving the meltability of glass, thus it is preferably not introduced.

In La₂O₃, Gd₂O₃, Y₂O₃ and Yb₂O₃, the component with the greatest impact on improving glass refractive index and maintaining glass stability is La₂O₃. However, if only La₂O₃ is used in the optical glass of the present invention, it is difficult to ensure the sufficient glass stability. Thus, the introduced amount of La₂O₃ in the present invention is the most, and La₂O₃ is made to coexist with Gd₂O₃; or preferably La₂O₃ and Gd₂O₃ are made to coexist with Y₂O₃; more preferably Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃+Yb₂O₃) is less than 0.2, further preferably Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is in the range of 0.01-0.15, and furthermore preferably Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is in the range of 0.05-0.12. The high-refractive index and low-dispersion glass with excellent glass stability can be obtained, while the glass is not easy to be colored.

Nb₂O₅ has an effect of improving glass refractive index and dispersion, as well as an effect of improving devitrification resistance and chemical durability of glass. However, when the content of Nb₂O₅ is less than 1%, the above effect cannot be reached; if the content exceeds 30%, the glass dispersion is improved, and the optical property of glass in the present invention cannot be reached, meanwhile the devitrification resistance of glass is deteriorated. Therefore, the content of Nb₂O₅ is 1-30%, preferably 2-25%, more preferably 3-20%, and further preferably 4-15%.

Ta₂O₅ can increase the refractive index and does better than Nb₂O₅ in maintaining the low dispersion of glass, and if the stability of glass requires further improvement, a small quantity of Ta₂O₅ can be introduced to replace part of Nb₂O₅. However, Ta₂O₅ is very expensive when compared with other components, hence, its usage is reduced in the present invention from the perspectives of utility and cost. The content of Ta₂O₅ in the present invention is 0-10%, preferably 0-5%, and more preferably not introduced.

TiO₂ can increase the refractive index as well and can be involved in the formation of glass network, the appropriate introduction of which can make glass stabler. Instead, the over content will significantly increase the dispersion of glass and decrease the transmittance of the short wave in the visible region, increasing the tendency of glass coloring. Therefore, the preferable content of TiO₂ in the present invention is 0-10%, more preferably 0.1-5%, and further preferably 0.5-3%.

When the introduced amount of Ta₂O₅ is reduced or Ta₂O₅ is not introduced as the glass components of the present invention, through the introduction of Nb₂O₅ or TiO₂, it is preferable to coexist TiO₂ and Nb₂O₅ as glass components, more preferably control TiO₂/Nb₂O₅ under 0.3, further preferably under 0.25 and more further preferably under 0.2, so as to enable the high refraction and low dispersion, and provide good stability of glass whilst effectively control the degree of pigmentation.

For the present invention, the refractive index and stability of glass can be improved through the introduction of a little ZrO₂ (0.5% or more); it will be difficult to melt glass and obtain uniform glass when the amount of ZrO₂ introduced exceeds 20%. Therefore, the content of ZrO₂ in the present invention is 0.5-20%, preferably 1-15%, and more preferably 3-10%.

The present invention preferably limits the introduced amount of Nb₂O₅ in glass components to be greater than or equal to that of ZrO₂, i.e., Nb₂O₅≥ZrO₂, to effectively suppress the glass coloring and improve the property of devitrification resistance. The more preferable range of Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) for the present invention is 0.4-0.8, further preferably 0.45-0.7 and more further preferably 0.48-0.6, which can further effectively suppress the glass coloring and increase the transmittance.

The present invention also preferably controls the ratio of the total amount of Nb₂O₅, Ta₂O₅ and ZrO₂ (Nb₂O₅+Ta₂O₅+ZrO₂) to the total amount of SiO₂ and B₂O₃(SiO₂+B₂O₃), that is, the preferable ratio range of (Nb₂O₅+Ta₂O₅+ZrO₂)/(SiO₂+B₂O₃) is less than 1, more preferably 0.1-0.9, further preferably 0.5-0.8, which can reach the preferable ranges of refractive index and Abbe number, as well as effectively suppress the glass coloring and increase the heat stability and devitrification resistance of glass.

WO₃ can increase the refractive index. If its content exceeds 10%, dispersion will be significantly increased, the transmittance on the long side of short waves in glass's visible region will be decreased and the tendency of coloring will be increased. Therefore, the preferable content of WO₃ in the present invention is 0-10%, more preferably 0-5%, further preferably 0-3%, and more further preferably not introduced.

Proper ZnO can improve the stability or meltbility of glass and the effect of compression molding, but its excessive content will reduce the refractive index which cannot meet the requirements of the present invention, decrease the devitrification resistance and increase the liquidus temperature of glass. Therefore, the preferable content of ZnO in the present invention is 0-15%, more preferably 0-10%, further preferably 0-5%, and more further preferably not introduced.

Among the components of glass, the preferable range of (ZnO+Y₂O₃)/La₂O₃ in the present invention is under 0.5, more preferably 0.05-0.3 and further preferably 0.08-0.15, which can be more favorable to improve the stability of glass and lower the transition temperature.

R₂O (R₂O is one or more of Li₂O, Na₂O or K₂O) can improve the meltbility and lower the transition temperature of glass, but when its content exceeds 10%, the stability of glass will become worse and the refractive index will be greatly decreased. Therefore, the preferable content of R₂O in the present invention is 0-10%, more preferably 0-5%, and further preferably not introduced.

RO (RO is one or more of BaO, SrO, CaO or MgO) can improve the meltbility and lower the transition temperature of glass, but when its content exceeds 10%, the devitrification resistance of glass will be lowered. Therefore, the preferable content of RO in the present invention is 0-10%, more preferably 0-5%, and further preferably not introduced.

By introducing a small amount of Al₂O₃, the stability and chemical stability of glass can be improved. However, when its content exceeds 10%, the glass will have a tendency to deteriorate the meltbility and lower the devitrification resistance. Therefore, the preferable content of Al₂O₃ in the present invention is 0-10%, more preferably 0-5%, and further preferably not introduced.

Bi₂O₃ can increase the refractive index of glass, but its excessive content will lower the transmittance on the long side of short waves in the visible region and show a tendency of coloring. Therefore, the preferable content of Bi₂O₃ in the present invention is 0-10%, more preferably 0-5% and further preferably not introduced.

GeO₂ can effectively improve the stability and devitrification resistance of glass as well. As GeO₂ is very expensive, the preferable content of GeO₂ is 0-10%, more preferably 0-5% and further preferably not introduced.

The clarification effect of glass can be increased by adding a little Sb₂O₃, SnO₂ and CeO₂. However, when the Sb₂O₃ content exceeds 1%, the glass will show a tendency of lowering the clarification property, and its strong oxidation promotes the deterioration of the shaped mould. Therefore, the preferable addition amount of Sb₂O₃ is 0-1%, more preferably 0-0.5%, and further preferably not added. SnO₂ can also be added as a clarifying agent, but when its content exceeds 1%, the glass will be colored, or when the glass is heated, softened, and molded for reshaping, Sn will become a starting point for nucleation, resulting in a tendency of devitrification. Therefore, the preferable content of SnO₂ in the present invention is 0-1%, more preferably 0-0.5%, and further preferably not added. The role and the proportion of the added amount of CeO₂ are consistent with SnO₂, so the preferable content of CeO₂ is 0-1%, more preferably 0-0.5%, and further preferably not added.

In addition, the raw materials of glass introduced in the form of nitrate, carbonate or sulfate can also increase the defoamability. In the present invention, one or more of Sb₂O₃, SnO₂ or CeO₂ can be combined with one or more of the above nitrate, carbonate or sulfate, being effective as well.

F is a component effectively lowering dispersion and reducing transition temperature of glass, but its excessive content will show a tendency of significantly decreasing the refractive index of glass or increasing the volatility of glass melt, forming texture when the glass melt is shaped, or increasing the refractive index changes due to volatilization. F, as a raw material, can be introduced with YF₃, LaF₃, YbF₃, ZrF₄, ZnF₂, alkali fluoride or alkaline earth fluoride. The percentage of F ion in the case of 100% total anion amount in glass can be taken into consideration for the introduced amount of F. Calculated by the percentage of anion, the preferable content of F in the present invention is 0-30%, more preferably 0-20%, and further preferably not introduced.

[Optical Properties of Optical Glass]

Hereinafter, the properties of the optical glass of the present invention will be described.

The optical glass of the present invention is a high-refraction low-dispersion glass, and a lens made of the high-refraction low-dispersion glass is combined with a lens made of high-refraction high-dispersion glass for chromatic aberration correction. The optical glass of the present invention has a glass refractive index in the range of above 1.85, preferably in the range of 1.87-1.91, more preferably in the range of 1.88-1.90, and further preferably in the range of 1.88-1.89, from the viewpoint of imparting optical properties suitable for its use. The range of the Abbe number ν_(d) of the glass of the present invention is in the range of 35-45, preferably in the range of 37-41 and more preferably in the range of 38-40.

[Coloring of Optical Glass]

The short-wave transmission spectrum characteristics of the glass of the present invention are represented by pigmentation degree (λ₇₀/λ₅). λ₇₀ refers to a wavelength corresponding to a glass transmittance of 70%, and λ₅ is a wavelength corresponding to a glass transmittance of 5%. The measurement of λ₇₀ is carried out using a glass having a thickness of 10±0.1 mm with two opposing planes parallel to each other and optically polished, measuring the spectral transmittance in the wavelength region from 280 nm to 700 nm and a wavelength exhibiting 70% of the transmittance. The spectral transmittance or transmittance is an amount indicated by I_(out)/I_(in) in the case where light of the intensity I_(in) is incident perpendicularly to the above surface of the glass, passes through the glass and emits light of the intensity I_(out) from one plane, including the transmittance of the surface reflection loss on the above surface of the glass. The higher the refractive index of the glass, the greater the surface reflection loss. Thus, in high refractive index glass, a small value of λ₇₀ means that the glass itself is colored very little.

The λ₇₀ of optical glass provided by the present invention is less than or equal to 410 nm, preferably less than or equal to 400 nm, more preferably less than or equal to 385 nm, further preferably less than or equal to 378-385 nm, and most preferably in the range of 378-380 nm.

Optical elements of imaging optical system or projection optical system with balanced and fine colors can be provided through making λ₇₀ less than or equal to 410 nm. In addition, due to the little coloring and high refractive index low dispersion, imaging optical system and projection optical system can be miniaturized. Based on this, the optical glass of the present prevention is suitable to be used as the optical element for constituting imaging optical system and projection optical system, especially as the optical element for constituting the exchanging lenses of single-lens reflex camera.

[Transition Temperature of Optical Glass]

The optical glass will gradually turn from solid state to plastic state within a certain temperature range. The transition temperature refers to the temperature at which the glass sample is heated from room temperature to the sag temperature, and the temperature corresponding to the intersection of the low temperature region and the straight line extension of the high temperature region.

The glass of the present invention has a transition temperature Tg of below 735° C., preferably 710-735° C. and more preferably 715-725° C.

[Chemical Stability of Optical Glass]

In the process of manufacture and use, the capability of the glazed surface of optical glass components to resist various erosion media effects becomes the chemical stability of the optical glass.

The water resistance durability Dw (powdered method) and acid resistance durability D_(A) (powdered method) of the glass provided by the present invention are above the category 2, preferably above the category 1.

The water resistance durability Dw (powdered method) is calculated as per the testing method specified in GB/T17129 according to the following formula: D _(W)=(B−C)/(B−A)*100

in which: Dw—the leaching percentage of the glass (%)

-   -   B—the mass of the filter and the sample (g)     -   C—the mass of the filter and the eroded sample (g)     -   A—the mass of the filter (g)

The water resistance durability Dw of the optical glass is classified as six categories as per the calculated leaching percentage.

Category 1 2 3 4 5 6 Leaching <0.04 0.04-0.10 0.10-0.25 0.25-0.60 0.60-1.10 >1.10 percentage (Dw)

The acid resistance durability D_(A) (powdered method) is calculated as per the testing method specified in GB/T17129 according to the following formula: D _(A)=(B−C)/(B−A)*100

in which: D_(A)—the leaching percentage of the glass (%)

-   -   B—the mass of the filter and the sample (g)     -   C—the mass of the filter and the eroded sample (g)     -   A—the mass of the filter (g)

The acid resistance durability D_(A) of the optical glass is classified as six categories as per the calculated leaching percentage.

Category 1 2 3 4 5 6 Leaching <0.20 0.20-0.35 0.35-0.65 0.65-1.20 1.20-2.20 >2.20 Percentage (D_(A))

[Density of Optical Glass]

The density of the optical glass is the mass per unit volume at a temperature of 20° C., expressed in g/cm³.

The density of the glass of the present invention is below 5.3 g/cm³, preferably 5.15-5.3 g/cm³ and more preferably 5.15-5.2 g/cm³.

II. Optical Preform and Optical Element

Hereinafter, the optical preform and the optical element of the present invention will be described.

The optical preform and the optical element of the present invention are both formed by the optical glass of the present invention described above. The optical preform of the present invention has a high refractive index and low dispersion. The optical element of the present invention has a high refractive index and low dispersion, which can provide optical elements such as various lenses and prisms having a high optical value at a low cost.

Examples of the lens include various lenses with spherical or aspheric surfaces, such as concave meniscus lens, convex meniscus lens, biconvex lens, biconcave lens, planoconvex lens, and planoconcave lens.

This lens is combined with a lens made of high-refraction high-dispersion glass to correct the chromatic aberration, suitable as a lens for chromatic aberration correction. In addition, the lens is also effective for the compactness of the optical system.

In addition, for the prism, due to the high refractive index, by combining in the optical system, you can achieve a compact wide-angle optical system through the curved optical path, towards the desired direction.

Embodiment

The present invention is explained by the following embodiments, but the present invention should not be limited to these embodiments.

[Optical Glass Embodiment]

Firstly, carbonate, nitrate, sulfate, hydroxide, oxide, boric acid and so on are applied to obtain a glass No. 1-35 of a composition shown in Tables 1-4; various raw materials corresponding to the composition of optical glass are weighed in proportion for fully mixing to obtain a mixed raw material; the mixed raw material is placed into a platinum made crucible to be heated to 1380˜1450° C., clarified and mixed for 3˜5 hours to become uniform molten glass, which is poured into the preheated module and is slowly cooled after being kept for 2˜4 hours at the temperature of 650˜700° C., then various optical glasses of glass No. 1-35 is obtained.

In addition, the characteristics of each glass are measured by the following methods, and the measurement results are shown in Tables 1 to 4.

(1) Refractive Index Nd and Abbe Number νd

The refractive index and Abbe number are measured as per the method specified in GB/T7962.1-2010.

(2) Pigmentation Degree of Glass (λ₇₀, λ₅)

The spectral transmittance is measured by using a glass sample having a thickness of 10±0.1 mm with two opposing planes optically polished, and calculated on the basis of the result.

(3) Transition Temperature of Glass (Tg)

To measure as per the method specified in GB/T7962.16-2010.

(4) Proportion (ρ)

To measure as per the method specified in GB/T7962.20-2010.

(5) Chemical Stability D_(W), D_(A)

To measure as per the testing method specified in GB/T17129 according to the Formula

TABLE 1 Embodiment Composition 1 2 3 4 5 6 7 8 9 10 B₂O₃ 18.56 7.26 9.34 15.3 15.2 14.25 14.21 11.2 9.16 14 SiO₂ 9.81 6.55 8.35 9.41 7.21 14.05 9.34 8.69 8.42 6.3 La₂O₃ 35.57 50 31.84 29.0 36.1 26.11 32.53 33.37 31 40.2 Gd₂O₃ 14.84 7.34 25.76 10.59 13.74 6.37 6.34 20.4 24.06 21.3 Y₂O₃ 8.87 5.61 1.82 2.17 3.05 5.68 1.52 9.4 2.73 1 Yb₂O₃ 0.16 1.85 3.67 0 5.21 4.17 2.74 3.22 0.87 0 ZrO₂ 2.31 2.64 3.54 5.12 2.52 6.33 3.15 1.23 2.37 6.6 Nb₂O₅ 8.03 6.31 6.14 17.71 8.99 9.36 18.09 3.62 11.47 9 Ta₂O₅ 0 3.25 2.57 1.00 0.74 4.17 2.14 4.51 1.25 0 TiO₂ 0.36 0.61 1.75 1.78 2.44 2.32 2.44 0.85 1.62 1.5 WO₃ 0 3.14 1.52 2.41 0 0.52 2.14 1.33 1.47 0 ZnO 0.74 2.33 0 0.78 2.12 0 4.03 0 2.73 0 R₂O 0 0.25 0.57 0 1.47 3.24 0 0 0 0 RO 0.32 0 1.82 2.03 0 0 0 1.00 1.52 0 Al₂O₃ 0 1.24 1.11 0.18 0 3.31 1.33 0.63 1.20 0 GeO₂ 0.23 0.62 0 1.44 0 0 0 0 0 0 Bi₂O₃ 0 0 0 1 1.05 0 0 0 0 0 Sb₂O₃ 0.2 0 0.2 0 0 0.12 0 0 0.13 0.1 SnO₂ 0 1 0 0 0.16 0 0 0.55 0 0 CeO₂ 0 0 0 0.08 0 0 0 0 0 0 F 0 0 1 0 0 0 2 0 0 0 SiO₂/(SiO₂ + B₂O₃) 0.346 0.474 0.472 0.381 0.322 0.496 0.397 0.437 0.479 0.31 Y₂O₃/(La₂O₃ + 0.149 0.087 0.029 0.052 0.052 0.134 0.035 0.142 0.047 0.016 Gd₂O₃ + Y₂O₃ + Yb₂O₃) Y₂O₃/(La₂O₃ + Gd₂O₃ + Y₂O₃) 0.15 0.089 0.031 0.052 0.058 0.149 0.038 0.149 0.047 0.016 TiO₂/Nb₂O₅ 0.045 0.097 0.285 0.101 0.271 0.248 0.135 0.235 0.141 0.167 Nb₂O₅/(Nb₂O₅ + TiO₂ + ZrO₂) 0.75 0.66 0.537 0.72 0.644 0.52 0.764 0.635 0.742 0.526 (Nb₂O₅ + Ta₂O₅ + ZrO₂)/(SiO₂ + 0.364 0.883 0.692 0.964 0.547 0.702 0.993 0.471 0.858 0.768 B₂O₃) (ZnO + Y₂O₃)/La₂O₃ 0.27 0.159 0.057 0.102 0.143 0.218 0.171 0.282 0.176 0.025 nd 1.875 1.904 1.895 1.883 1.869 1.892 1.910 1.904 1.896 1.884 vd 37.68 37.09 38.33 38.27 39.64 38.47 38.14 38.26 40.25 39.22 λ70 384 385 382 378 384 384 379 380 381 380 ρ (g/cm³) 5.1961 5.241 5.231 5.204 5.198 5.221 5.207 5.235 5.195 5.17 Tg 719 727 723 724 719 724 728 730 725 721 (° C.) D_(W) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 D_(A) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1

TABLE 2 Embodiments Composition 11 12 13 14 15 16 17 18 19 20 B₂O₃ 13.91 3.35 14.38 19.24 15.47 11.37 14.4 15.24 12.34 13.24 SiO₂ 9.22 2.16 10.39 5.21 9.55 7.88 3.52 9.14 7.39 7.94 La₂O₃ 31.15 49.15 44.69 30.5 32.47 32.79 40.56 35.54 42.26 37.83 Gd₂O₃ 26.68 21.5 11.01 9.12 18 19.37 10.08 9.4 13.39 12.41 Y₂O₃ 3.12 12 7.36 4.91 3.25 4.79 6.37 7.14 4.15 5.58 Yb₂O₃ 1.25 0 0 1.33 0 0 2.54 0 0 1.2 ZrO₂ 2.36 1 2.17 2.14 3.11 3.14 4.98 4.11 5.14 6.26 Nb₂O₅ 5.14 1 4.52 15.54 6.17 10.65 12.4 13.15 7.36 8.34 Ta₂O₅ 1.64 2.15 0 4.71 0 0 0 0 1.52 0.34 TiO₂ 1.21 0.1 1.31 3 1.67 1.39 0.94 0.62 1.32 1.74 WO₃ 2.64 0 1.31 0 0 0 0 0 0.74 0.67 ZnO 0 1.47 0 1.54 2.14 2.68 1.74 3.21 1.52 1.47 R₂O 0 0 1.47 0 1.22 3.04 0 0 0 0.54 RO 0.53 3.03 0 2.66 0 0 2.37 0 1.32 0 Al₂O₃ 1.00 0 1.19 0 4.31 1.33 0 1.71 0 0 GeO₂ 0 2.71 0 0 2.54 1.47 0 0.64 1.35 2.14 Bi₂O₃ 0 0 0 0 0 0 0 0 0 0 Sb₂O₃ 0.15 0 0 0 0.1 0 0 0.1 0 0 SnO₂ 0 0.38 0 0.1 0 0.1 0 0 0.2 0.3 CeO₂ 0 0 0.2 0 0 0 0.1 0 0 0 F 0 0 0 0 0 0 0 0 0 0 SiO₂/ 0.399 0.392 0.419 0.213 0.382 0.409 0.196 0.375 0.375 0.375 (SiO₂ + B₂O₃) Y₂O₃/(La₂O₃ + 0.05 0.145 0.117 0.107 0.06 0.084 0.107 0.137 0.069 0.098 Gd₂O₃ + Y₂O₃ + Yb₂O₃) Y₂O₃/ 0.051 0.145 0.117 0.11 0.06 0.084 0.112 0.137 0.069 0.1 (La₂O₃ + Gd₂O₃ + Y₂O₃) TiO₂/Nb₂O₅ 0.235 0.1 0.29 0.193 0.271 0.131 0.076 0.047 0.179 0.209 Nb₂O₅/ 0.59 0.476 0.565 0.751 0.563 0.702 0.677 0.735 0.533 0.510 (Nb₂O₅ + TiO₂ + ZrO₂) (Nb₂O₅ + Ta₂O₅ + 0.395 0.753 0.27 0.916 0.371 0.716 0.97 0.708 0.711 0.705 ZrO₂)/ (SiO₂ + B₂O₃) (ZnO + Y₂O₃)/La₂O₃ 0.1 0.274 0.165 0.211 0.166 0.228 0.2 0.291 0.134 0.186 nd 1.874 1.918 1.895 1.905 1.911 1.875 1.867 1.863 1.885 1.894 vd 39.34 37.01 38.67 37.69 37.12 41.08 39.67 38.45 39.17 37.69 λ70 379 378 379 381 382 382 381 379 380 379 ρ (g/cm³) 5.224 5.236 5.199 5.210 5.207 5.226 5.225 5.218 5.206 5.215 Tg (° C.) 718 716 719 718 719 717 716 724 719 723 D_(W) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 D_(A) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 2 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1

TABLE 3 Embodiment Composition 21 22 23 24 25 26 27 28 29 30 B₂O₃ 12.34 12.3 15.33 14.47 13.64 13.37 14.32 13.68 12.39 14.22 SiO₂ 9.99 7.14 6.39 9.98 8.06 7.16 6.37 6.19 5.94 6.85 La₂O₃ 38.1 40.6 36.83 31.97 35.62 31.42 35.33 41.93 39.45 36.64 Gd₂O₃ 15.44 19.22 16.47 17.22 19.53 18.86 11.54 15.59 14.68 16.34 Y₂O₃ 4.31 4.39 3.91 4.18 9.45 8.49 9.53 4.26 9.29 4.18 Yb₂O₃ 0 0 0 0 0 0 1.36 0 0 0 ZrO₂ 4.36 3.42 5.44 7.33 4.18 7.66 4.15 6.47 5.39 6.38 Nb₂O₅ 7.62 9.14 8.27 10.17 8.24 9.37 7.18 8.34 8.65 7.19 Ta₂O₅ 1.36 0 0 0 0 0 3.67 0 0 0 TiO₂ 1.39 1.64 1.39 0.37 1.28 0 1.64 1.39 0.85 1.4 WO₃ 0 0 0 0 0 0 0 0 0 0 ZnO 0 2.15 2.47 0 0 0 2.44 0 0 2.37 R₂O 0 0 2.16 0 0 0 0 0 0 0 RO 0 0 0 0 0 0 0 0 0 0 Al₂O₃ 2.41 0 1.34 4.31 0 0 2.47 0 0 2.69 GeO₂ 2.68 0 0 0 0 3.67 0 2.15 3.36 1.74 Bi₂O₃ 0 0 0 0 0 0 0 0 0 0 Sb₂O₃ 0 0 0 0 0 0 0 0 0 0 SnO₂ 0 0 0 0 0 0 0 0 0 0 CeO₂ 0 0 0 0 0 0 0 0 0 0 F 0 0 0 0 0 0 0 0 0 0 SiO₂/ 0.447 0.367 0.294 0.408 0.371 0.349 0.308 0.312 0.324 0.325 (SiO₂ + B₂O₃) Y₂O₃/(La₂O₃ + 0.075 0.068 0.068 0.078 0.146 0.144 0.165 0.069 0.146 0.031 Gd₂O₃ + Y₂O₃ + Yb₂O₃) Y₂O₃/ 0.075 0.068 0.068 0.078 0.146 0.144 0.169 0.069 0.146 0.073 (La₂O₃ + Gd₂O₃ + Y₂O₃) TiO₂/Nb₂O₅ 0.182 0.179 0.168 0.036 0.155 0 0.228 0.167 0.098 0.195 Nb₂O₅/ 0.57 0.644 0.548 0.569 0.601 0.55 0.554 0.515 0.581 0.480 (Nb₂O₅ + TiO₂ + ZrO₂) (Nb₂O₅ + Ta₂O₅ + 0.597 0.646 0.631 0.716 0.572 0.83 0.725 0.745 0.766 0.644 ZrO₂)/ (SiO₂ + B₂O₃) (ZnO + Y₂O₃)/La₂O₃ 0.113 0.161 0.173 0.131 0.265 0.27 0.339 0.102 0.235 0.179 nd 1.896 1.892 1.890 1.887 1.893 1.895 1.892 1.889 1.890 1.888 vd 39.47 38.94 39.16 39.55 39.62 38.69 39.16 39.34 38.99 40.09 λ70 378 379 380 378 381 382 379 378 382 379 ρ (g/cm³) 5.231 5.124 5.206 5.135 5.119 5.134 5.233 5.141 5.135 5.128 Tg (° C.) 718 717 721 718 720 722 716 720 719 718 D_(W) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 2 gory 1 gory 1 gory 1 gory 1 gory 1 gory 1 gory 2 gory 1 D_(A) Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 2 gory 1 gory 2 gory 1 gory 1 gory 1 gory 1

TABLE 4 Embodiment Composition 31 32 33 34 35 B₂O₃ 13.2 13.6 14.0 14.0 14.0 SiO₂ 6.5 6.6 6.5 6.5 6.5 La₂O₃ 45.0 45.5 39.3 39.5 36.9 Gd₂O₃ 12.0 13.5 17.2 16.0 22.0 Y₂O₃ 6.0 4.0 6.5 7.0 4.6 Yb₂O₃ 0 0 0 0 0 ZrO₂ 5.5 6.3 6.6 6.0 6.1 Nb₂O₅ 9.3 9.0 8.0 8.5 8.3 Ta₂O₅ 0 0 0 0 0 TiO₂ 1.5 1.5 1.9 1.5 1.6 WO₃ 0 0 0 1.0 0 ZnO 1.0 0 0 0 0 R₂O 0 0 0 0 0 RO 0 0 0 0 0 Al₂O₃ 0 0 0 0 0 GeO₂ 0 0 0 0 0 Bi₂O₃ 0 0 0 0 0 Sb₂O₃ 0 0 0 0 0 SnO₂ 0 0 0 0 0 CeO₂ 0 0 0 0 0 F 0 0 0 0 0 SiO₂/(SiO₂ + B₂O₃) 0.33 0.327 0.317 0.317 0.317 Y₂O₃/(La₂O₃ + 0.095 0.064 0.103 0.112 0.072 Gd₂O₃ + Y₂O₃ + Yb₂O₃) Y₂O₃/(La₂O₃ + 0.095 0.064 0.103 0.112 0.072 Gd₂O₃ + Y₂O₃) TiO₂/Nb₂O₅ 0.161 0.167 0.238 0.176 0.193 Nb₂O₅/(Nb₂O₅ + 0.571 0.536 0.485 0.531 0.519 TiO₂ + ZrO₂) (Nb₂O₅ + Ta₂O₅ + 0.751 0.757 0.712 0.707 0.702 ZrO₂)/(SiO₂ + B₂O₃) (ZnO + Y₂O₃)/La₂O₃ 0.156 0.088 0.165 0.177 0.125 nd 1.886 1.882 1.8880 1.887 1.883 vd 39.47 38.94 39.16 39.55 39.62 λ70 378 379 380 378 381 ρ (g/cm³) 5.131 5.124 5.206 5.135 5.119 Tg(° C.) 718 717 721 718 720 D_(W) Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 1 gory 1 D_(A) Cate- Cate- Cate- Cate- Cate- gory 1 gory 1 gory 1 gory 1 gory 1

[Optical Preform Embodiment]

The optical glass obtained in Embodiment 1 in Table 1 is cut into a predetermined size, and a release agent made of boron nitride powder is uniformly coated on the surface, and then is heated and softened to be press-molded to produce a concave meniscus lens, a convex meniscus lens, a biconvex lens, a biconcave lens, a planoconvex lens, a planoconcave lens, and other various lens and prism preforms.

[Optical Element Embodiment]

The preforms obtained in the above-mentioned optical preform embodiment are annealed for fine-tuning while the deformation inside the glass is reduced, so that the optical characteristics such as the refractive index are brought to the desired values.

Then, each of the preforms is ground and polished, and a variety of lenses and prisms such as concave meniscus lens, convex meniscus lens, biconvex lens, biconcave lens, planoconvex lens, and planoconcave lens are prepared. An anti-reflection film may be coated on the surface of the obtained optical element.

The present invention provides a high-refraction low-dispersion optical glass having a low cost and excellent transmittance, with glass refractive index of more than 1.85 and Abbe number of 35-45, and an optical element made of the glass, which can meet the demands of modern novel photoelectric products. 

The invention claimed is:
 1. An optical glass comprising by weight percentage: B₂O₃: 1-30%; SiO₂: 0-20%; La₂O₃: 25-55%; Gd₂O₃: 5-40%; Y₂O₃: 0-25%; Yb₂O₃: 0-10%; Ta₂O₅: 0-10%; Nb₂O₅: 1-30%; TiO₂: 0-10%; TiO₂/Nb₂O₅: less than 0.25; ZrO₂: 0.5-20%; WO₃: 0-10%; ZnO: 0-15%; (ZnO+Y₂O₃)/La₂O₃: less than 0.5; R₂O: 0-10%, in which R₂O is at least one of Li₂O, Na₂O or K₂O; RO: 0-10%, in which, RO is at least one of BaO, SrO, MgO or CaO; Al₂O₃: 0-10%; GeO₂: 0-10%; Bi₂O₃: 0-10%; the glass contains no PbO; the glass has a refractive index of from 1.88 to 1.91, and an Abbe number of 35-45, wherein Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) is 0.4-0.519; (Nb₂O₅+Ta₂O₅+ZrO₂)/(SiO₂+B₂O₃) is 0.6-0.768; and Nb₂O₅ is greater than ZrO₂.
 2. The optical glass according to claim 1, optionally containing at least one of: Sb₂O₃: 0-1%; SnO₂: 0-1%; or CeO₂: 0-1%.
 3. The optical glass according to claim 2, wherein B₂O₃: 5-25%; SiO₂: 0.1-15%; La₂O₃: 30-52%; Gd₂O₃: 5-35%; Y₂O₃: 1-20%; Ta₂O₅: 0-5%; Nb₂O₅: 2-25%; TiO₂: 0.1-5%; ZrO₂: 1-15%; WO₃: 0-5%; ZnO: 0-10%; R₂O: 0-5%; RO: 0-5%; Al₂O₃: 0-5%; GeO₂: 0-5%; Bi₂O₃: 0-5%; Sb₂O₃: 0-0.5%; SnO₂: 0-0.5%; and CeO₂: 0-0.5%.
 4. The optical glass according to claim 1, wherein SiO₂/(SiO₂+B₂O₃) is below 0.5; Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is below 0.2, and (ZnO+Y₂O₃)/La₂O₃ is in the range of 0.05-0.3.
 5. The optical glass according to claim 1, wherein SiO₂/(SiO₂+B₂O₃) is 0.25-0.4; Y₂O₃/(La₂O₃+Gd₂O₃+Y₂O₃) is 0.05-0.12; Nb₂O₅/(Nb₂O₅+TiO₂+ZrO₂) is 0.48-0.519; and (ZnO+Y₂O₃)/La₂O₃ is of 0.08-0.15.
 6. The optical glass according to claim 1, wherein WO₃: 0-4%.
 7. The optical glass according to claim 1, wherein the glass has an Abbe number from 37 to
 41. 8. The optical glass according to claim 1, wherein the glass has a refractive index from 1.88 to 1.90, and an Abbe number from 38 to
 40. 9. A glass preform made of the optical glass according to claim
 1. 10. An optical element made of the optical glass according to claim
 1. 